On Board Diagnostics II (OBD II) was brought about to monitor an automobile's electronics system by providing a single point interface for diagnostic equipment. For example, an engine control module, a transmission control module and a suspension control module can all be accessed through a single OBD II connector. The OBD II standard was developed as a cooperative effort between the Society of Automotive Engineers (S.A.E.), the EPA and the California Air Resources Board (C.A.R.B.). Its installation and usage was made mandatory on all vehicles sold in the U.S. starting on Jan. 1, 1996 as an attempt to standardized automobile diagnostic testing and monitoring.
The automobile's engine control module manages the engine and optimizes fuel economy and power output while controlling emissions. When the engine control module detects a fault in one its engine sensors, it will illuminate an “check engine” light on the dashboard. A technician can collect information on sensors and actuators for shorts, open circuits, lazy sensors (slow responding) and out-of-range values by attaching a diagnostic device to the OBD II port and retrieve information about the fault.
The automobile's control modules are mini-computers having computer subsystems. There is a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), data busses and control lines. The ROM contains microcode or firmware, which is a set of instructions especially written for each automobile that are executed by the CPU.
Whenever two or more electronic apparatus are connected via cabling, voltage variations, voltage spikes and ground loops can be introduced and damage the automobile electrical systems and the attached testing equipment. A ground loop is a current, generally unwanted, in a conductor connecting two points that are supposed to be at the same ground potential (voltage), but are actually at different potentials. For example, a ground loop occurs when an automobile's chassis connects to a first earth ground and its ground potential is zero volts. A piece of testing equipment such as engine analyzer also connects to earth ground, but its ground potential is at a positive 5 volts relative to the ground at the chassis. The analyzer's probe ground lead is then attached to the chassis and a difference of 5 volts between the grounds produce a current to flow through the ground wires causing damage to the testing equipment and/or the automobile's electronics. Ground loops can also generate noise into the test system's cabling corrupting data transmissions.
Therefore what is needed is a vehicle control interface device that electrically isolates a vehicle's OBD II communication signals from attached analyzers which is capable of high speed rate transmission.